| Popis: |
Publisher Summary This chapter discusses the reliability of an adhesive and its impact on the performance of an electronic assembly. The major failure modes of adhesives include loss of adhesion, high thermal impedance, loss of electrical contact, and corrosion. Sloughing of particles from the adhesive during vibration is also known to damage wire bonds, ?ne wires, and thin-?lm metallization in sealed packages, causing opens or shorts, depending on the type of particle. Long-term reliability requires maintaining adhesion strength after repeated thermal cycling, elevated-temperature exposure, or temperature–humidity exposure. Mechanical reliability for die or substrate attachment over time may be determined by comparing die-shear strength or lap-shear strength before and after aging or after exposure to actual- or accelerated-stress conditions. Low-modulus adhesives produce low bending stresses and have higher radii of curvature than intermediate- or high-modulus adhesives. The radius of curvature of parts bonded with low-modulus adhesives increases with the size of the die. It is found that the absorption of moisture in under?ll adhesives induces a tensile hygrothermal stress on the solder-ball connections causing electrical opens in the connections and cracking in the adhesive. |
